The present invention relates to delivering hydrogen peroxide at a variable rate to a consumer unit, in particular to a unit for bleaching paper pulp forming part of a plant for the production of paper pulp.
The hydrogen peroxide concentrations in question are concentrations by weight, in solution in water.
Provision has already been made to generate in situ the hydrogen peroxide consumed by a unit for bleaching paper pulp, this peroxide being conveyed directly by pipe from the generation apparatus to a bleaching unit.
However, this technique frequently presents the following problem: the bleaching unit requires a hydrogen peroxide rate which varies within a range considerably greater than the flexibility of the generation apparatus.
The rates in question here are rates reduced to the 100% concentration of hydrogen peroxide.
The aim of the invention is to overcome this difficulty. To this end, the subject-matter of the invention is a method for supplying hydrogen peroxide having a predetermined concentration C1 to a unit which consumes hydrogen peroxide at a variable rate R, in particular a unit for bleaching paper pulp, characterized in that:
hydrogen peroxide having a concentration C2 greater than or equal to the value C1 is generated on the site of the consumer unit or in the immediate proximity of this site;
the hydrogen peroxide thus generated is temporarily stored in at least one holding tank; and
hydrogen peroxide is drawn from the holding tank at a variable rate which, optionally after dilution, corresponds to the said rate R and is fed to the consumer unit.
The method according to the invention can comprise one or more of the following characteristics:
in the event of the liquid level in the holding tank falling to a predetermined low level, hydrogen peroxide having in particular a concentration C3 markedly greater than the value C1 is drawn from a back-up tank, is optionally diluted with water to the concentration C1 and is fed to the consumer unit;
for supplying a consumer unit which accepts hydrogen peroxide having a concentration C3 markedly greater than the value C1, in the event of the liquid level in the holding tank falling to a predetermined low level, hydrogen peroxide having the concentration C3 is drawn from a back-up tank and is fed to the consumer unit;
the rate consumed R varies from 0 to a value R1 and the rate generated varies between two values R2 and R3 such that R3xe2x88x92R2 less than R1;
the values R2 and R3 respectively represent 50 and 110% approximately of a nominal hydrogen peroxide generation rate NR, whereas the value R1 represents approximately 400% of this NR value;
the value C2 is between 2 and 45% approximately and in particular between 15 and 30% approximately, whereas the value C3, when a back-up tank is used, is between 45 and 80% approximately.
Another subject-matter of the invention is a plant intended for the implementation of a method as defined above, this plant comprising:
an apparatus for the generation of hydrogen peroxide at a concentration C2;
at least one holding tank connected via a pipe to the generation apparatus; and
a unit which consumes hydrogen peroxide at a variable rate R, connected via a pipe to the holding tank.
According to other characteristics of this plant:
the plant additionally comprises a back-up tank which contains hydrogen peroxide at a concentration C3 which is in particular markedly greater than the concentration C1 of the hydrogen peroxide consumed by the consumer unit and which is connected to the latter via another pipe;
the plant additionally comprises a dilution apparatus inserted between the back-up tank and the consumer unit;
the dilution apparatus is also inserted between the generation apparatus and the consumer unit.